... but not details. The principle is entirely physiological: The central
portion of the retina (fovea), where detailed vision occurs, has a low sensitivity to the color blue. It is very difficult, and very tiring, to distinguish details (such as type) that are outlined in shades of pure blue. For this reason, blue text, thin blue lines, and small blue things generally should be avoided. Blue makes an ideal background color, however. Registered by the rest
of the retina, it provides an excellent contrast to detailed central elements
in analogous or monochromatic shades.